In ship construction, space and weight are important and often critical factors which must be taken into account in the engineering design of the vessel and all apertinent structures. Ladders presently employed aboard ship are constructed in conventional manner with treads of sufficient width to accommodate both feet of a user standing upon the tread, the treads being supported by two or more stringers extending between the upper and lower levels interconnected by the ladder way. In ascending or descending a ladder, the right foot of a user steps upon the right hand portion of a first tread and the left foot steps upon the left hand portion of a second tread. Thus, alternate treads are employed by each foot of the user and it is not usually necessary to stand upon a single tread with both feet during ascent or descent of a ladder. The presence of a full width tread in conventional ship ladders, only half of the tread being used, is wasteful of material and adds to the weight of the ladder structure. The presence of a full width tread also presents an obstacle to the movement of a user's foot in ascending or descending the ladder creating an unnecessary safety hazard for the user. The inclination of a conventional ladder must be such that a user can move his foot past the unused portion of a tread in moving to the next tread of the ladder, thus limiting the angle of inclination.
Ladders are known in which treads or rungs are alternately arranged along a single stringer or pole. In ascending and descending ladder of this known type, a user must face the ladder and support himself by holding on to the rungs to guide his ascent or descent. Such ladders of known construction cannot be descended facing forward, as with a stairway. These known ladders also require a fair degree of dexterity on the part of a user and are not very comfortable to use.